Quorum quenching by endophytic Bacillus cereus AL1: a lactonase-based anti-virulence strategy against Pseudomonas aeruginosa

Abstract

BACKGROUND: Pseudomonas aeruginosa infections are often challenging to treat due to multiple drug resistance, besides the development of biofilms and a plethora of virulence factors regulated by quorum sensing. Quorum-quenching enzymes, such as N-acyl homoserine lactonases, represent a promising anti-virulence strategy by disrupting this signaling mechanism without exerting selective pressure, leading to resistance. This study aimed to screen endophyte and epiphyte isolates for lactonase activity and evaluate their potential to inhibit virulence in Pseudomonas aeruginosa. RESULTS: Fifty-two bacterial isolates (42 endophyte and 10 epiphyte) were isolated from ten plants. The aiiA gene encoding lactonase enzyme was detected in 11 endophytes and one epiphyte isolate, among which nine showed complete degradation (100%) of the quorum sensing signal molecule N-hexanoyl-L-homoserine lactone. The partially purified lactonase enzyme from the endophyte Bacillus cereus AL1 isolate exhibited significant anti-virulence activity, reducing biofilm formation, swarming motility, and pyocyanin production against Pseudomonas aeruginosa PAO1 and clinical Pseudomonas aeruginosa isolates. Sequence alignment of the Bacillus cereus AL1 lactonase protein revealed close similarity to the homologous lactonase from Bacillus cereus. The quorum quenching activity of the partially purified lactonase AL1 provided protection in a Galleria mellonella infection model. CONCLUSION: The study highlights the potential of Bacillus cereus AL1 lactonase as an effective anti-virulence agent against Pseudomonas aeruginosa without the pressure for resistance development.